It would be great to get even more granular and get to the county level to show how even the "divided" counties are purple as well. My guess is that you might get some counties that are 100% Red or 100% Blue.
These colors are great, but almost ultraviolet to my eyes. I can only look at the map for 5 seconds. Also, the color doesn't really tell me how far from 50/50 the states are.
The burning, it hurts. I think the purple is like #17f00017f or something. Seriously, you can't just mix RGB like this; perceptual color scales like Cynthia Brewer has helped popularize are the right choice. http://colorbrewer2.org/
The first thing I noticed on your map (which is really nice, by the way) was that it's far more divisive than the per-state version. Most interesting.
I think this just highlights what people have been saying for quite a while now, that the political divide in this country isn't red states versus blue states, but urban versus rural. If you go to a level that separates those, as per-county does but per-state doesn't, you see a much bigger divide.